Generally, ABS (acrylonitrile-butadiene-styrene) resin has a good balance of properties such as impact resistance, chemical resistance, heat resistance, and mechanical strength as well as processability, and is easily molded such that it has been widely used for various products such as parts of automobiles, housings of electrical/electronic appliances, and the like, in addition to small household and personal items/amenities.
Recently, demand has increased for a thermoplastic resin having both low gloss and soft touch surface, which is different from the typical characteristics of conventional solid and glossy plastics. Particularly, demand is increasing for a thermoplastic resin having both low gloss and soft touch surface for the production of products that people often touch or see over a long period of time, such as interior parts of automobiles and housings of electrical/electronic appliances. Furthermore, because of strict regulations protecting the environment, there is also an increasing need for a low gloss resin which is prepared without a coating process and which is directly moldable.
There are three methods for preparing a low gloss ABS resin. One widely used method includes adding a non-gloss additive-matting agent, such as an inorganic filler, an acrylic resin or a cross-linked styrene resin, to the ABS resin. Another method removes gloss during a post processing procedure. This method can provide a low gloss effect by etching a molded product during an injection molding process or by a coating process. Another method forms a microscale rough surface by controlling the size of rubber particles of a dispersed phase in an ABS resin. Such a microscale rough surface may have low gloss by scattering incident light.
Although the method of obtaining a low gloss effect using the additive-matting agent can be convenient, there is a drawback in that homogeneous gloss may not be obtained depending on the distribution of the additive. The method of etching a molded product during an injection molding process or a coating process can increase production costs and is not environmentally friendly. Although the method of forming a rough surface by controlling rubber particle size has an advantage in that the method does not need an additional process step, it also has a drawback in that both low gloss property and soft touch surface cannot be obtained at the same time.
In order to lower resin gloss, U.S. Pat. No. 5,475,053 employs a spherical graft copolymer as a matting agent, and U.S. Pat. No. 4,652,614 employs a spherical graft copolymer containing rubber in an amount of about 5 to about 80% as a matting modifier. Additionally, U.S. Pat. No. 4,668,737 uses spherical rubber particles having a core/shell structure of about 0.05 to about 20 μm to reduce gloss, and U.S. Pat. No. 5,237,004 uses a polymer particle of about 2 to about 15 μm.
However, when using additives containing rubber particles, there may be problems of peeling, deterioration of physical properties, and partial high gloss, in addition to high production cost. Further, since the resins have a dense structure, as compared to rubber particles prepared by bulk polymerization or solution polymerization, it is difficult to obtain a soft touch surface using the same.
U.S. Pat. No. 5,605,963 and EP 0668319 disclose an ABS resin having large rubber particles in order to obtain low gloss and impact resistance at the same time. However, even though the ABS resins may have low gloss, the resins do not have a modified surface with soft touch.
Japanese Patent No. 3,673,084 and Japanese Patent Laid-open Publication No. 2000-141322 disclose the use of wood flour to modify surface texture. It can be difficult, however, to mold the resin at conventional molding temperatures.